Bottom line: the car officially requires an unobtanium Castrol OE oil (it appears that in the past year Amsoil may have come up with one that straight-up complies). Most dealers don't sell it (some don't want to, others just get massive drum and can't sell it).

That leaves the unlucky few (like me) to resort to ebay to source it at $10+ a quart. Which, BTW, is cheaper per quart than what the few dealers that do sell it sell it for.

For fear of warranty denials, I stuck to that ridiculous requirement during the warranty period. When the warranty expired, I did a baseline Blackstone lab test on the used OE Castrol, and went with Mobil1 EP - a motor oil that by nearly all accounts complies with the spec.

Ultimately, that hard-to-meet spec seems to relate to long oil service intervals anyway. LR's interval is 15k miles, which as we know, is dumb. I happen to put at most 7.5k miles/year (nowadays more like 5k/year), so the yearly change is plenty frequent enough to effectively not have to worry about any of this nonsense provided a use a decent quality oil.

I have a leftover quart of the unobtanium Castrol OE oil. The last oil change, I filled with only Mobil1 EP.

For the next oil change, can I use up that quart and fill the rest with Mobil1 EP? They are the same 5W-20 weight.

Isn't oil mixed when adding a quart ? I know when my cars are low and I add a quart I go to the local gas station (usually Mobil) and get a quart that meets the requirements of the manufacturer. I have no idea what type & weight of oil the dealer is putting in my cars